2) 0,64⋅49; 4)√40⋅√10-√20/√5.

2) 0,64⋅49

$$ \sqrt{0.64 \cdot 49} = \sqrt{0.64} \cdot \sqrt{49} = 0.8 \cdot 7 = 5.6 $$

4)√40⋅√10-√20/√5

$$\sqrt{40} \cdot \sqrt{10} - \frac{\sqrt{20}}{\sqrt{5}} = \sqrt{40 \cdot 10} - \sqrt{\frac{20}{5}} = \sqrt{400} - \sqrt{4} = 20 - 2 = 18$$

Ответ: 2) 5.6; 4) 18